This invention relates to a squeezing and chamfering device to be used with a screw-thread roll-forming machine for producing a tapered screw-threaded portion at an end of a gas pipe or a joining section of the same.
Heretofore, an end of a gas pipe or a joining section thereof has been processed to form a tapered screw thread b on the outer surface of an opening end a.sub.1 of a pipe as shown in FIG. 1. However, since the tapered screw-thread b is formed by use of a die, the thickness of the end portion a.sub.1 becomes excessively thin, thereby causing deficiency in the strength of the end portion a.sub.1. Furthermore, since the structure of the material of the pipe is cut-formed by the die, the strength of the threaded portion tends to be reduced.
Otherwise, the tapered screw-thread b has been formed on the end portion a.sub.1 of the pipe a as shown in FIG. 2 by use of a tapered thread roll-forming machine. According to this method, since the thread b is formed by pressing a rolling die onto the surface of a tapered portion, the structure of the material of the pipe and hence the strength of the threaded portion of the pipe are not damaged. However, the roll-forming machine is ordinarily constructed so that the roll-forming operation is carried out only after a tapered portion c has been formed at an opening end a1 of the pipe and an end surface d of the tapered portion c has been chamfered.
Forming the tapered portion c and chamfering the end surface d, however, have been ordinarily effected separately, and therefore, the thread-forming operation of gas pipe has been found to be extremely troublesome, and saving of the labor cost due to a large-scale production has been thereby made difficult.